The present invention relates to a camshaft adjuster which, in a hydraulically adjustable manner and according to a vane-type motor principle, may adjust the camshafts of an internal combustion engine relative to a further shaft, such as for example the crankshaft.
There are many different types of camshaft adjusters. The most frequently used type of adjuster, at the date of filing of the present application, is that which works according to the vane-type motor principle. Two wheels which are movable relative to one another, a stator and a rotor, which are positioned coaxially, together form hydraulic chambers of which at least two chambers are contra-rotating. With the increase of the one chamber, the camshaft attached to the rotor by a central screw (other types of fastening being also known) is moved in the advanced direction, for an advanced opening time of the gas exchange valves, whilst with the increase of the other contra-rotating hydraulic chamber the camshaft is moved in the retarded direction relative to the other shaft, for a retarded opening time of the gas exchange valve. The regions denoted as hydraulic chambers may also be denoted more simply as hydraulic regions. The hydraulic medium is displaced into the various hydraulic regions via channels. In this regard, for example, channel guides are known to the applicant, in which individual channel portions are firstly guided along the camshaft itself and are transferred to the camshaft adjuster in a region of a camshaft passage of the camshaft adjuster. The channels then lead to the individual hydraulic regions, partially located within the rotor and completely surrounded by the same rotor material.
Rotor-driven hydraulic channel portions are known from U.S. Pat. No. 6,439,183 (Denso Corporation), which issued from an application filed on Oct. 1, 2001. As shown primarily in FIGS. 3, 5 and 6 of U.S. Pat. No. 6,439,183 the hydraulic channel portions allow connections to the hydraulic regions which all extend on the rotor surface and are covered by the stator inner wall. It is apparent that rotors of camshaft adjusters which have a similar appearance to those disclosed in U.S. Pat. No. 6,439,183, come from an extruded profile by cutting off along the planar faces of the retarded rotor, the channels being inserted into the planar faces of the rotor by milling. Tests on camshaft adjusters produced in this manner led to high amounts of leakage of the hydraulic medium, such as for example engine oil, primarily in the full load range. Thus unnecessary energy of the internal combustion engine is used to pump the engine oil which has escaped into the oil sump back into the hydraulic chambers. In tests, leakage rates of one liter have been shown at an operating pressure of 3 bar. In particular, during hot idling such an adjuster is shown to be the main point of oil leakage.
In addition, the patent family with the members U.S. Pat. No. 6,363,897 B (INA WÄLZLAGER SCHAEFFLER OHG), which issued from an application filed on Dec. 22, 2000, and DE 19962981 A (INA WÄLZLAGER SCHAEFFLER OHG), filed Dec. 24, 1999, discloses in its second embodiment a circular sealing washer to seal the inner chamber within the stator. The seals are located in the outer walls of the adjuster. The openings in the outer walls of the camshaft adjuster are sealed relative to the rotating parts by the leakage seals present in the walls.
Camshaft adjusters with rotors, whose channels extend completely within the rotor, are frequently provided with round drilled elongate channels. The round cross-sectional shape of the channel requires a larger drilled diameter at the same decrease in pressure as the aforementioned channel shape. The shape of the channel may produce a greater decrease in pressure which is undesirable, as decreases in the channel pressure also have a negative effect on the degree of hydraulic efficiency.